What do starfish eat?

December 2006

These multiarmed animals eat almost anything that moves slower than they do.

If a sea star loses an arm, it can grow a new one through a process known as regeneration.

Sea stars are successful scavengers and predators. Some are carnivorous, attacking mollusks like mussels and oysters, which are stationary animals. Others feed on dead fish or other carrion, and some take in organisms from seawater.

Carnivorous sea stars have an interesting feeding behavior. When feeding on a mollusk, such as a clam, the sea star slowly climbs onto its prey’s shell. Using its hundreds of tiny tube feet on the underside of its body, it steadily exerts pressure its prey’s hard exterior. Some species can apply as much as 12 pounds of pressure. When the prey’s shell opens the tiniest bit, the sea star everts its stomach through its mouth and slips it into its prey’s soft interior and the feasting begins.

Like its tiny tube feet, the mouth of sea stars is on the underside of its body. These animals have no brain, just a simple nervous system, which relays impulses from arm to arm. Around the mouth is a nerve ring, which connects to radial nerves in each arm. At the tip of each arm are delicate sensors that detect food or chemicals.

Because some mollusks, such as oysters and mussels, anchor themselves for life, an attack by sea stars on a bed of these stationary animals can be devastating. Another sea star, the voracious crown-of-thorns (Acanthaster planci), which ranges from the Red Sea throughout the Indian and Pacific oceans and to the Pacific coast of Panama, feeds on live coral. In some areas, this voracious predator has completely wiped out coral populations.

In recent years, starfish have been more correctly renamed “sea stars,” because they are not fish. They are echinoderms and related to sand dollars, sea urchins and sea cucumbers.